1. Field of the Invention
The invention relates to packing elements of the type that are often called “random” or “dumped” packings, and will be described with particular reference thereto. However, it will be appreciated that the elements have applications in other areas.
2. Discussion of the Art
Random or dumped packings are used to fill towers units in which mass or heat transfer or any chemical reaction processes occur. A particularly important application is the use of such ceramic elements in heat recovery operations where it is necessary to provide maximum effective contact with hot fluids passing through the reactor. Another key factor in maximizing efficiency is the maintenance of as low a pressure difference between top and bottom of the tower as possible. To ensure this the packing elements should present the minimum resistance to flow. This is promoted by very open structures but open structure alone is of limited use if the elements in the tower nest together such that parts of one packing element penetrate within the space of a second element. It is therefore important that the design of the elements minimize the tendency of the elements to nest together. Another particularly important application is as a bed topping material which is intended to keep material within a bed confined with limited ability to be entrained in a gas flow or to be caused to move around by such a flow. Such entrainment or abrasion typically causes significant losses to the material in the bed.
Ceramic packing elements can be produced by an extrusion or a dry-pressing process and hence have an essentially uniform cross-section along one axial direction which provides an axis of symmetry for the element. Several such shapes have been described in the art ranging from the very simple to the complex. All are based on an essentially cylindrical shape and differ basically in the internal structure within the cylindrical shape. The simplest structure is a basic cylinder with no internal structure at all. This type of structure is often called a Raschig ring and has been known for many years. At the other end of the complexity scale are the structures described in U.S. Design Pat. No. 455,029 and U.S. Pat. No. 6,007,915. Between the extremes there are simple wagon-wheel shapes such as are described in U.S. Pat. Nos. 3,907,710 and 4,510,263. Others show deformed cylindrical structures, such as those described in U.S. Pat. No. 5,304,423. BE 481 212 discloses a packing element for use in heat exchangers, distillation towers, catalyst supports, and the like having four through passages and an indented exterior surface. DE 24 25 058 discloses a ceramic filling material with a cylindrical or hexagonal shape and multiple through passages. U.S. Pat. No. 2,172,714 discloses a stackable block for regenerators.
For certain applications, such as bed limiters, the pressure drop is less important since the thickness of the bed limiter layer is relatively small. It is far more important that the packing elements do not nest together and still allow free passage of gases while being heavier that the elements comprising the bed on which the packing elements rest and whose extent is thereby limited.